The present invention relates to an optical drilling device using a laser beam, having an optical arrangement located in the beam path for guiding the laser beam along a circular cutting path, as well as a focusing lens positioned downstream from the arrangement which focuses the laser beam onto a workpiece.
In a known optical device of this type, a laser beam, used for example to drill spray holes in injection nozzles, is guided along a circular path having a desired radius, known as the trepanning radius, which largely corresponds to the desired drill hole radius. Changing the direction of the main beam makes it possible to vary the angle of incidence of the laser tool and thus the conical shape of the drill hole.
A variety of devices have been proposed for setting the desired trepanning radius and the angle of incidence. In one known device, an eccentrically rotating focusing lens is provided. In this case, the angle of incidence cannot be varied separately. Mechanical unbalance as well as the need to set parameters in the rotating system also present difficulties
A device having an eccentrically rotating focusing lens and a tiltable plane-parallel plate is also known in which the angle of incidence can be additionally influenced by tilting. The mechanism that must also be moved is complex, and mapping errors are difficult to avoid.
A further device of this type has a rotating, tilted plane-parallel plate as well as an adjustable wedge plate positioned upstream from a stationary or rotating focusing lens. In this case as well, the parameters need to be set in the rotating system, and the mechanism is complex and subject to imbalance.
The object of the present invention is to provide an optical device of the type mentioned in the preamble which offers simplified and highly accurate setting capabilities as well as a simple design.
This object is achieved with the features of claim 1. According to these features, the optical arrangement includes a separately rotatable image rotator that is used to guide the beam along the cutting path.
According to these features, separate functions are provided for guiding the beam along the cutting path, setting the trepanning radius and angle of incidence, and focusing the beam so that these settings can be made without difficulty. This also yields a simple drive mechanism in which imbalance can be easily avoided.
According to one advantageous design of the device, the optical arrangement has a shifting element and/or a tilting element, and the image rotator is designed as a prism, mirror or anamorphote device. The shifting element and tilting element can be used to easily adjust the angle of incidence and trepanning radius, respectively. The construction can also be easily implemented by designing the shifting element as a tiltable, plane-parallel plate, designing the tilting element as an adjustable wedge plate, tilting mirror or adjustable lens, and designing the image rotator as a Dove prism or Abbe-Kxc3x6nig prism.
Focusing spots can be minimized by connecting a telescope upstream from the focusing lens system to expand the beam.
The design is further improved by arranging the shifting element, tilting element, and image rotator consecutively in the beam direction.
Maintaining a simple design, automatic focusing can be achieved by providing an autofocus mechanism in which the image rotator is used as an image derotator in a back-reflected beam, and the shifting and tilting motions achieved by the shifting element and tilting element, respectively, are reversed. To avoid extraction losses, focusing can take place on a different wavelength.
A further important advantage of the features according to the present invention is the improved roundness of the drill holes. The cutting beam produced by the laser frequently does not have a perfect rotational symmetry in its intensity distribution, e.g., due to optical aberrations or the oscillations stimulated in multiple laser modes. In trepanning lens systems without an image rotator, the orientation of the focus asymmetry changes during trepanning relative to the cutting direction. This can lead to roundness irregularities in the drilling result. The image rotator, on the other hand, causes the asymmetrical focus to also rotate during cutting, thus improving roundness.